Technical Field
The invention relates to an array antenna, in particular to a waveguide slotted array antenna.
Description of Related Art
In recent years, high-sensitivity, broadband, low-profile, low sidelobe and high-performance array antennas have the characteristics of multi-frequency band and low cost, and thereby are widely applied to the technical fields such as radar, communication, remote sensing and measuring, spatial technology and the like. Micro-strip array antennas and waveguide slotted array antennas are mainly used at present.
Micro-strip array antennas have the characteristics of being low in profile, low in cost, light, easy to machine, etc.; however, when the frequency or the antenna array scale is increased, the insert loss of the micro-strip array antennas is increased due to the conductor loss and dielectric loss. Therefore, the micro-strip array antennas can achieve broad bands, but cannot achieve high frequency, high efficiency or high gains.
For waveguide slotted array antennas, one or more slots are formed in the conductor wall of a waveguide tube to cut off current lines on the inner wall, part of currents on the surface of the waveguide inner wall can bypass the slots, the other part of the currents flow through the slots in the original direction in the displacement current form, and thus radiation is generated by power lines at the slots. The waveguide slotted array antennas have the characteristics of low conductor loss, high efficiency, stable performance and the like. Existing waveguide slotted array antennas include waveguide slotted traveling wave array antennas and waveguide slotted standing wave array antennas. The beam pointing of the waveguide slotted traveling wave array antennas change along with the frequency, consequentially, the beam pointing of the antennas is inconsistent within a broadband range, the antennas can only be used within an extremely narrow bandwidth range, and the frequency band cannot be widened; as the waveguide slotted standing wave array antennas are essentially resonant antennas, electric performance indexes such as the directional pattern and the sidelobe level can deteriorate severely once the frequency deviates from the resonant frequency, and thus the waveguide slotted standing wave array antennas can be used only within a narrow frequency band range, and the bandwidth is inversely proportional to the array antenna scale.
With the increase of the radar anti-interference requirement and the development of the modern electronic industry, antennas are required to have the performance of low sidelobes or extremely low sidelobes. A traditional waveguide slotted array antenna comprises a feed layer and a radiation layer, and two schemes are mainly used for lowering sidelobes of the traditional waveguide slotted array antenna. For one scheme, energy distribution of the radiation layer is adjusted by adjusting the power distribution proportion of the feed layer, and thus the sidelobes are lowered; however, by adoption of the scheme, the main lobe is generally widened and the gain is reduced while the sidelobes are lowered, and extremely low sidelobes cannot be achieved on the basis of ensuring a narrow main lobe and avoiding the gain loss. For the second scheme, a polarization layer is additionally arranged on the radiation layer to lower sidelobes, specifically, through the polarization layer, the polarization direction of an electric field can deflect in the rotating direction of a metal strip, the energy of a square array antenna in the diagonal direction can well distributed conically, and then the antenna can rotate by 45 degrees around a spindle; through the polarization layer at the angle of 45 degrees, directional patterns of the E plane and the H plane of antennas can be optimized, and low sidelobes achieved; however, during volume production, the cost of antennas can be increased by 20%. In addition, the waveguide wide sides of traditional waveguide slotted array antennas are inversely proportional to the frequency, the wide sides are large under a low frequency, and consequentially small sizes of antennas cannot be ensured; in addition, the machining and welding requirements for feed and radiation array surfaces are high, and consequentially, the machining precision cannot be ensured, and volume production cannot be achieved easily.